/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 86187
 * Date: 2022-04-18
 * Time: 20:50
 */

//Scanner scan = new Scanner(System.in);

import java.util.Scanner;

public class Test_4_18 {

    /**
     * 递归求 第 n 个斐波那契数列 （不推荐）
     * 1 1 2 3 5 8 13 21 34 55
     * @param n
     * @return
     */
    public static int fibonacci(int n) {

        if(n == 1 || n == 2) {
            return 1;
        }

        return fibonacci(n - 1) + fibonacci(n - 2);
    }

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        int n = scan.nextInt();

        int ret = fibonacci(n);

        System.out.println(ret);

    }
}
